Combine first 3 ingredients; cut in 2/3 cup butter with a pastry blender or 2 knives until crumbly. Stir in jalapeño. Add buttermilk, stirring just until dry ingredients are moistened.
Turn out dough onto a lightly floured surface, and knead lightly 3 or 4 times. Pat or roll dough to 1/2" thickness; cut with a 2 1/2" round cutter. Place on a lightly greased baking sheet.
Bake at 425° for 16 to 18 minutes or until golden. Brush with melted butter, if desired, before serving.